Microelectro Mechanical Systems (MEMS) is a multi-disciplinary research frontier developed based on micro electronic technique, which is a technology for manufacturing microelectronic devices using semiconductor process. Compared with conventional electro-mechanical devices, MEMS devices have significant advantages of high temperature resistance, small sizes, and low power consumption. After several decades of developments, MEMS has been one of the most important scientific and technological fields of the world, which may relate to various subjects and techniques, such as electricity, mechanics, material, physics, chemistry, biology and medicine, and have a broad application prospect.
A pressure sensor is a transducer for converting a pressure signal to an electrical signal. There are mainly two types of pressure sensor according to operational principle, including resistance type and capacitive type. The capacitive pressure sensor may work to measure pressure by changing capacitance between a top electrode plate and a bottom electrode plate using pressure.
FIG. 1 schematically illustrates a cross-sectional view of a capacitive pressure sensor according to a conventional art. The capacitive pressure sensor includes a substrate 10, a fixed electrode plate 20 formed in the substrate and a movable electrode plate 30 formed above the substrate 10. A cavity 40 is formed by the substrate 10, the movable electrode plate 30, together with a sealing ring 35 disposed between the substrate 10 and the movable electrode plate 30. The movable electrode plate 30 is disposed relative to the fixed electrode plate 20, which constitute a capacitor. The movable electrode plate 30 may move towards the fixed electrode plate 20 under pressure, leading to a change of a capacitance value. Thus, a pressure value may be obtained by measuring a capacitance value. However, the distance between the movable electrode plate and the fixed electrode plate is the most crucial part to the pressure sensor. Specifically, the pressure sensor would have a narrow measuring range if the distance is too small; alternatively, the pressure sensor would have a lowed measuring precision if the distance is too great.
A conventional oscillator may have a structure similar to that shown in FIG. 1. By alternately applying a forward or reverse voltage to the movable electrode plate and the fixed electrode plate, the movable electrode plate may oscillate close to or away from the fixed electrode plate. As for this type of oscillator, if the distance between the movable electrode plate and the fixed electrode plate is too great, a higher voltage is required to drive the oscillator to oscillate. But if the distance is too small, the oscillator would have a narrow oscillation range.